This invention relates to displays and, more particularly, to electrical circuitry for the correction of nonuniformity in a cathode ray tube (CRT) having red, green, and blue phosphors for presenting an image in color.
CRTs are widely used for the presentation of data in many forms. In some applications, it is important to present the data with high accuracy in respect to both the color and the brightness of the data. For example, CRT's which are used for previewing or color correction must provide accurate color presentation. In particular, the display of a white screen should show no coloring or hues.
Color CRT's are usually constructed with three electron guns which direct electron beams respectively at red, green, and blue phosphors located on the viewing screen. Modulation of the intensity of these beams shifts a region of the display from a uniform white to a color, and also changes the brightness of the screen. An apertured mask is placed between the screen and the guns, the apertures guiding a bundle of three beams simultaneously to the requisite phosphors. An electromagnetic coil or yoke scans the bundle of the three beams across the screen. Red, green, and blue video signals are applied to electrodes of the respective guns for modulation of the intensities of the respective beams.
A problem arises in that, as a result of the manufacturing process, some nonuniformity results from insufficient levels of cleanliness or irregularities in the size of the phosphor dots and possibly in the apertured mask. There results a nonuniformity in the display which, while possibly being acceptable for situations such as the home-viewing of movies, is excessively troublesome where accurate presentation is required.